At times it is desirable to sidetrack (deviate) existing well bores for various reasons in producing a more economical well bore. It is well known in the oil and gas industry that whipstocks are used in drilling to direct or deviate a drill bit or cutter at an angle from a well bore. The well bore can be cased (lined with pipe) or uncased (open hole; not lined with pipe). It has been customary to follow plug and abandonment (P&A) procedures when using a whipstock. These P&A procedures vary as to cased or uncased well bores. Most P&A procedures follow OCS guidelines as the operator does not want communication between the "old" well bore and the "new" bore. OCS guidelines would not be followed where the operator is drilling additional "drain" bores in an existing well. For the cased well bore, the operator will set a cement plug in the well bore (100 hundred feet thick at a minimum) followed by a bridge plug or EZ-drill plug. The bridge plug is a wire line device which is set three to five feet above the casing collar (or joint) near the required point that deviation of the well bore is needed. The position of the bridge plug and the whipstock is critical because the deviated hole must NOT penetrate the casing at or near a casing collar (or joint). The whipstock is traditionally set several feet above the bridge plug. Great care is exercised to coordinate wire line and pipe measurements to assure that the whipstock is clear of the casing collar (or joint). In an uncased hole, only a cement plug of the proper length is used. The length of the plug is determined by the depth of the uncased hole to the point at which the deviation is required. The downhole tool is traditionally set above the cement plug.
The complete downhole assembly generally consists of the whipstock assembly attached to some form of packer assembly. There are presently two conventional whipstock types available, the "Packstock" and the "Bottom Trip". The Packstock is a whipstock and a packer assembly that is combined to form a single downhole unit. The bottom trip device is a single whipstock with a plunger, sticking out of the bottom of the downhole tool, which when set down on the bottom of the hole, will release a spring loaded slip or wedge within the whipstock which in turn holds the tool in place. The whipstock is the actual oil-tool that causes the drill bit or cutter to deviate from the well bore. The packer is another oil-tool that holds the whipstock in place once the whipstock has been set in the well bore at the desired orientation. This packer is given the name anchor packer and it is this packer that rests above the bridge plug in a cased hole and above the cement plug in an uncased hole. In the case of the bottom trip whipstock, it is the bridge plug that forces the plunger to release the spring loaded slips or wedges; thus, holding the tool in place. It should be apparent that there are two fundamental types of packer in use; the first operates in a cased hole and the second operates in an uncased hole. The bottom trip device operates only in a cased hole; it is an old device; and, it is fraught with problems because it has only a single slip or wedge which can work loose.
The whipstock is a triangularly shaped tool about 10 to 12 feet long. It is slightly less then the diameter of the well bore at its bottom and slopes so that its diameter approaches infinitely at its top. The back of the tool usually rests against the low side of the well bore, where the low side of the well bore is defined as that side of the hole most affected by gravity. The tool face is cup-shaped and guides the hole drilling equipment off to the side of the hole in the direction set by the orientation of the tool face. The bottom of the tool is attached to the packer.
Traditionally the whipstock must be chosen for each well bore so that its bottom diameter matches the well bore and the packer, if used. Its top end must match the inside diameter of the well bore so that the drilling equipment sees a smooth transition off to the side of the hole; and the back of the tool should match the internal diameter of the well bore. In addition the cupped face of the tool has been chosen to match the bore size in order to properly guide the drilling equipment. This means that the oil or gas field operator must keep a stock of different whipstocks to match the various standard well bores used in the industry.
This invention standardizes the whipstock tool to three varieties to fit hole sizes from 33/4 inches up to 121/2 inches. The invention proposes one style of whipstock for use with both mechanically set packers and hydraulically set packers. And finally, the invention proposes an apparatus and method for retrieval of the valuable and expensive downhole assembly after the deviated hole is completed. This retrievable whipstock would be invaluable in multiple drain holes in a single well bore and would be used in both cased and open hole (uncased) conditions.